The present disclosure generally relates to eye tracking, and specifically relates to using time-of-flight based depth information for eye tracking in virtual reality and/or augmented reality applications.
Eye tracking refers to the process of detecting the direction of a user's gaze, which may comprise detecting the angular orientation of the eye in three-dimensional space. Eye tracking may further comprise detecting the location of the eye (e.g., the center of the eye), the torsion (i.e., the roll of the eye about the pupillary axis) of the eye, the shape of the eye, the current focal distance of the eye, the dilation of the pupil, other features of the eye's state, or some combination thereof. One known technique for eye tracking is capturing video images of a user and identifying the orientation of the user's pupils using a machine vision algorithm. However, this technique requires substantial computing resources, and is susceptible to occlusion of the eye by eyelashes and eyelids. Furthermore, this method is dependent on the contrast between the iris and the pupil, which is not invariant across users. Thus, video based pupil tracking may not be able to accurately track the eyes of certain users. Similarly, this technique may place constraints on the proximity of the camera to the user's eye. Furthermore, this technique may perform poorly when the camera is located off the axis of the user's gaze. However, when eye tracking is used in an HMD, it may be preferred that the detection element of the eye tracking system be small, be close to the eye, and be off the axis of the user's gaze.